The present invention relates to an aluminum alloy product having improved fatigue failure resistance. This invention further relates to an aluminum-zinc-magnesium-copper alloy having improved fatigue failure resistance over AA 7055.
The financial success of airlines depends upon a number of factors including the cost and performance of their aircraft. Aircraft manufacturers are actively engaged in producing aircraft that efficiently use high performance materials, low cost manufacturing technologies and low cost, advanced design concepts in order to lower the acquisition cost and/or increase the range and weight carrying capacity of their aircraft products.
Another important cost factor for airlines is the aircraft operating cost. Included in the operating cost is the cost of periodic safety inspection of aircraft components for structural damage. An aircraft usually requires two types of inspections: initial inspection and periodic inspection during the operating life of the aircraft. Each type of inspection is very costly, particularly the periodic inspection because the aircraft must be taken out of service for the inspection to be performed. Inspections may require detailed visual inspection and extensive non-destructive testing of exterior and interior structures.
High strength structural components which excel in durability and damage tolerance are highly desired by aircraft manufacturers. Durability and damage tolerance can translate into a long interval between initial inspection and the first periodic inspection and long repeat periodic inspection intervals. Aluminum alloy structural components (such as fastened joints) that exhibit high cycle fatigue performance and fatigue crack growth resistance can translate into long inspection intervals for aircraft.
Thus a need exists for 7000 series alloys that have desirable strength, toughness and corrosion resistance properties and also have improved fatigue failure resistance. A need also exists for aircraft structural parts that exhibit improved fatigue failure resistance.